1. Field of the Invention
The present invention relates generally to cancer vaccines that include an adjuvant, and to cancer vaccine adjuvants alone. In particular, the invention relates to cancer vaccine adjuvants derived or obtained at least in part from biological tissues, particularly extracellular matrix materials, such as from the small intestinal mucosa. The invention also relates to the field of methods for immunizing an animal against cancer using a cancer vaccine preparation that includes an extracellular matrix tissue-derived adjuvant. The invention also relates to the field of methods for preparing cancer vaccine adjuvants, as a method for preparing a cancer vaccine adjuvant from extracellular matrix tissue for vaccines to immunize an animal against cancer, particularly prostate cancer, is provided.
2. Related Art
Vaccination for the treatment of cancer is receiving increasing attention. Vaccines for melanoma, prostate and breast cancers have undergone development to include human clinical trials. Most of these vaccines utilize specific proteins to directly immunize the patient or to pulse harvested dendritic cells prior to infusion into the patient. Some trials have also used inactivated allogenic cancer cells grown in vitro.
In general, cancer vaccines have been administered without an adjuvant or with specific cytokines included as adjuvants. An adjuvant is defined as a compound which enhances the immune response to a vaccine immunogen(s).
There have been some reports of the use of a mycobacterial adjuvant with normal non-malignant cells. For example, use of human prostate cells in the treatment of prostate cancer is described in U.S. Pat. No. 6,972,128 (Dalgleish et al.). In particular, an allogeneic immunotherapeutic agent containing immortalized normal (non-malignant) human prostate cells (replication incompetent) is described. A mycobacterial adjuvant was used with a non-malignant murine melanoma cell preparation in a vaccine suitable for intra-dermal injection. These preparations were reported to provide some protection against murine tumor cell growth.
A combination of aluminum hydroxide and aluminum phosphate (collectively referred to as alum) is currently used in commercial vaccines as adjuvants for human and veterinary applications (11, 12). The efficacy of alum in increasing antibody responses to diphtheria and tetanus toxins is well established and HBsAg vaccine has been adjuvinated with alum. While the usefulness of alum is well established for some applications, it has limitations. For example, alum is ineffective for influenza vaccination and inconsistently illlicits cell mediated immune response. The antibodies elicited by alum-adjuvinated antigens are mainly of the IgG1 isotope in the mouse, which may be optimal for protection by some vaccinal agents.
Bacterial vaccines have also been described that include an adjuvant, typically alum. Because alum is particularly efficient at stimulating Th2 antibody responses to co-administered immunogens, and because effective cancer immunity relies heavily on Th1 cell-mediated immunity, alum is not typically included in cancer vaccines. Clearly, cancer vaccination would benefit from a method to provide general enhancement of the immune response to cancer immunogens.
Noscapine has been described as an adjuvant for vaccines, as well as for use in the treatment of tumors and cancer, in U.S. Pat. No. 7,090,852. Noscapine is an alkaloid from opium, and is available as a commercial byproduct in the commercial production of prescription opiates.
Recombinant, single immunogen cancer vaccines have also been described. One such product in Phase 3 clinical trials is the GVAX® vaccine (Cell Genesys, Inc., South San Francisco, Calif.). This cancer vaccine is used in patients with advanced-stage, hormone-refractory prostate cancer, and is comprised of two allogeneic prostate cancer cell lines that have been genetically modified to secrete granulocyte-macrophage colony stimulating factor (GM-CSF). This hormone plays a role in stimulating the body's immune response to the cancer vaccine. The cells are irradiated for safety (3). Cancer vaccination with the GVAX product has demonstrated a median increases in survival in cancer patients receiving the vaccine of approximately 7 months (4).
Though some studies have utilized specific cytokines as cancer vaccine adjuvants, such as GM-CSF in the GVAX vaccine (4), those cytokines typically enhance only specific features of the immune response and may be unstable outside of very controlled storage conditions (13, 14).
Pure soluble, recombinant and synthetic antigens, despite their better tolerability, are unfortunately often much less immunogenic than live or killed whole organism vaccines. Thus, the move towards the development of safer subunit vaccines has created a major need for more potent adjuvants. In particular, there is an urgent need for adjuvants capable of boosting cellular (Th1) immunity with a more acceptable toxicity.
Despite the description of over one hundred adjuvants in the scientific literature, alum remains the only adjuvant approved for human use in the USA (Petrovsky, 2006). Unfortunately, alum has no effect on cellular immunity and is faced with increasing concerns regarding potential for cumulative aluminium toxicity. There is a major unmet need for a safe efficacious adjuvant capable of boosting cellular plus humoral immunity.
The prerequisites for an ideal cancer adjuvant differ from conventional adjuvants for many reasons. First, the patients that will receive the vaccines are immuno-compromised because of, for example, impaired mechanisms of antigen presentation, non-responsiveness of activated T cells and enhanced inhibition of self-reactivity by regulatory T cells. Second, the tumor antigens are usually self-derived and are, therefore, poorly immunogenic. Third, tumors develop escape mechanisms to avoid the immune system, such as tumor immunoediting, low or non-expression of MHC class I molecules or secretion of suppressive cytokines. Thus, adjuvants for cancer vaccines need to be more potent than for prophylactic vaccines, and consequently may be more toxic, and may even induce autoimmune reactions.
To heighten the immune response to cancer antigens, researchers often attach a decoy substance, or adjuvant, that the body will recognize as foreign. Such adjuvants are often proteins or bacteria which “trick” the immune system into mounting an attack on both the decoy and the tumor cells. Other adjuvants act to stimulate specific effector cells within the immune system. Several adjuvants are described below:
Keyhole limpet hemocyanin (KLH) is a protein made by a shelled sea creature found along the coast of California and Mexico known as a keyhole limpet. KLH is a large protein that both causes an immune response and acts as a carrier for cancer cell antigens (Bandandi, et al, 2006(52); Redfern et al, 2006(53)). Cancer antigens often are relatively small proteins that may be invisible to the immune system. KLH provides additional recognition sites for immune cells known as T-helper-cells and may increase activation of other immune cells known as cytotoxic T-lymphocytes (CTLs).
Bacillus Calmette Guerin (BCG) is an inactivated form of the tuberculosis bacterium. BCG is added to some cancer vaccines with the hope that it will boost the immune response to the vaccine antigen (Totterman, 2005(54); Mosolits, 2005(55)). It is not well understood why BCG may be especially effective for eliciting immune response. However, BCG has been used for decades with other vaccines, including the vaccine for tuberculosis.
Interleukin-2 (IL-2) is a protein made by the body's immune system that may boost the cancer-killing abilities of certain specialized immune system cells called natural killer cells. Although it can activate the immune system, many researchers believe IL-2 alone will not be enough to prevent cancer relapse. Several cancer vaccines use IL-2 to boost immune response to specific cancer antigens (Wei, 2006 (57); He, 2005 (56), Rousseau, 2006(58)).
Granulocyte Monocyte-Colony Stimulating Factor (GM-CSF) is a protein that stimulates the proliferation of antigen-presenting cells and has been used as an adjuvant in a prostate cancer vaccine (Simons, 2006 (59)).
SIS is a commercially available accellular extracellular matrix (ECM) preparation produced from porcine small intestinal submucosa. SIS is a naturally derived, extracellular matrix, that is not synthetic or cross-linked. A commercial form of this collagenous acellular material is available from Cook Biotech, and is known by the trade name, “Oasis®”. In this product, SIS is taken from a biological source and is processed to remove all cells. This product is biocompatible and safe for human use.
SIS has found substantial utility as a tissue growth scaffold. For example, SIS has shown wide utility in urology (15-22), wound care and repair (23-24), as an anal fistula plug (25), tendon repair, and bone healing (26-27, 29, 31-33). Following implantation, SIS rapidly attracts mononuclear inflammatory cells followed by ingrowth of host tissue (FIG. 1). In this way, SIS serves as a scaffold for tissue repair (26-28). The SIS then becomes fully replaced by host tissue. Other extracellular matrices, such as porcine renal capsule material, behave in a similar fashion to SIS (29-30).
Canine prostate cancer cells have been reported to maintain their invasive phenotype when grown on SIS in culture (44). Studies in Lobund-Wistar rats have shown that SIS does not inherently promote growth of cancer in vivo (39). Despite these observations, SIS has not been proposed in any anti-cancer applications.
A need continues to exist in the medical arts for materials that may be used to enhance and/or improve existing clinical alternatives to the treatment of cancer, particularly to improve existing forms of cancer vaccines and cancer vaccine adjuvants with improved immunogenicity.